/Engine/Source/Runtime/Renderer/Public/PrimitiveSceneInfo.h
Builds an array of all primitive scene info's in this primitive's attachment group. This only works on potential parents (!LightingAttachmentRoot.IsValid()) and will include the current primitive in the output array.
void GatherLightingAttachmentGroupPrimitives ( [TArray](API\Runtime\Core\Containers\TArray)< const [FPrimitiveSceneInfo](API\Runtime\Renderer\FPrimitiveSceneInfo) *, SceneRenderingAllocator > & OutChildSceneInfos ) const